Treatment of congestive heart failure with electrical stimulation, and associated systems and methods

ABSTRACT

Systems and methods for treating congestive heart failure with high frequency stimulation are disclosed. A representative method for treating a patient includes applying an electrical signal having a frequency of from about 1 kHz to about 100 kHz to the patient via a treatment system that includes a signal delivery element in electrical communication with the patient&#39;s vagus nerve at a portion of the vagus nerve located at or proximate to the anterior interventricular junction of the patient&#39;s heart. The method can further include automatically detecting at least one physiological parameter of the patient, automatically determining at least one of an ejection fraction of the patient&#39;s heart and a correlate of the ejection fraction based on the detected parameter, and automatically adjusting the applied signal based on the determined ejection fraction.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to pending U.S. Provisional Application No. 62/286,892, filed Jan. 25, 2016, and is incorporated herein by reference.

TECHNICAL FIELD

The present technology is directed generally to treatment of congestive heart failure with electrical stimulation, and associated systems and methods.

BACKGROUND

Congestive heart failure (CHF) is a chronic condition characterized by a reduction in contraction strength (e.g., contractility) of one or both of the main pumping chambers of the heart—the left and right ventricles. Reduced contractility of the ventricles reduces the volume of blood ejected by each ventricle per heart beat (e.g., stroke volume). When this occurs, the heart cannot pump blood with normal efficiency, and blood and other fluids begin to build up within the cardiovascular system and other parts of the body, such as the lungs, liver, abdomen, and lower extremities. In some cases of CHF, the myocardium (e.g., heart muscle tissue) becomes so weakened that the ventricles stretch or dilate, thereby damaging the Purkinje fibers located in the walls of the ventricles. The Purkinje fibers are responsible for carrying the contraction impulse to the myocardium of the ventricles, and thus damage to the Purkinje fibers by the dilated ventricles compromises the electrical conduction system of the heart and reduces the synchronization of contractility, further compromising the ejection fraction. Accordingly, there is a need for systems and methods for treating congestive heart failure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are anterior and posterior views, respectively, of a human heart.

FIG. 2A is a partially schematic illustration of an implantable treatment system positioned to deliver electrical signals to the heart in accordance with several embodiments of the present technology.

FIG. 2B is a partially schematic illustration of a portion of an implantable treatment system positioned to deliver electrical signals to the heart in accordance with several embodiments of the present technology.

FIG. 3 is a flow diagram illustrating a method for treating congestive heart failure in accordance with an embodiment of the present technology.

FIG. 4 is a flow diagram illustrating a method for determining a representative (e.g., maximum) treatment amplitude in accordance with an embodiment of the present technology.

FIG. 5 is a flow diagram illustrating a method for adjusting a treatment signal in response to real-time ejection fraction feedback in accordance with an embodiment of the present technology.

DETAILED DESCRIPTION

The present technology is directed generally to systems for treating congestive heart failure (CHF), and in particular, to systems for treating CHF by improving contraction strength of the left and/or right ventricles via electrical stimulation. In one embodiment, the present technology includes a treatment system having an implantable signal generator and a signal delivery element configured to apply an electrical signal to a parasympathetic nerve innervating a portion of a patient's heart. The system includes one or more real-time feedback mechanisms for evaluating the efficacy of the applied signal and automatically adjusting the applied signal based on the efficacy. For example, in some embodiments the treatment system can automatically determine an ejection fraction of the patient's heart and adjust one or more parameters of the applied electrical signal based on the ejection fraction.

Definitions of selected terms are provided under heading 1.0 (“Definitions”). General aspects of the anatomical and physiological environment in which the disclosed technology operates are described below under heading 2.0 (“Introduction”) with reference to FIGS. 1A and 1B. An overview of the treatment systems in which the disclosed technology operates is described below under heading 3.0 (“Overview”) with reference to FIGS. 2A and 2B. Particular embodiments of the technology are described further under heading 4.0 (“Representative Embodiments”) with reference to FIGS. 3-5. Additional embodiments are described under heading 5.0 (“Additional Embodiments).

1.0 Definitions

As used herein, “vagus nerve” refers to any of the following: portions of the left vagus nerve, the right vagus nerve, and/or the cervical vagus nerve, branches of the vagus nerve such as the superior cardiac nerve, superior cardiac branch, and inferior cardiac branch, and the vagus trunk. Similarly, stimulation of the vagus nerve is described herein by way of illustration and not limitation, and it is to be understood that in some embodiments of the present technology, other autonomic and/or parasympathetic nerves and/or parasympathetic tissue are stimulated, including sites where the vagus nerve innervates a target organ, vagal ganglia, nerves in the epicardial fat pads, a carotid artery, a jugular vein (e.g., an internal jugular vein), a carotid sinus, a coronary sinus, a vena cava vein, a pulmonary vein, and/or a right ventricle, for treatment of heart conditions or other conditions.

As used herein, “high frequency” or “HF” refers to a frequency of from about 1 kHz to about 100 kHz, or from about 1.2 kHz to about 100 kHz, or from about 1.5 kHz to about 100 kHz, or from about 2 kHz to about 50 kHz, or from about 3 kHz to about 20 kHz, or from about 3 kHz to about 15 kHz, or from about 5 kHz to about 15 kHz, or from about 3 kHz to about 10 kHz, or 1 kHz, 2 kHz, 3 kHz, 4 kHz, 5 kHz, 8 kHz, 9 kHz, 10 kHz, 11 kHz, 12 kHz, 15 kHz, 20 kHz, 50 kHz, or 100 kHz. As used herein, the term “about” refers to values within +/−10% of the stated value. Moreover, as used herein, “low frequency” or “LF” refers to a frequency less than about 1 kHz.

As used herein, “real-time” refers to within 10 seconds or less, within 5 seconds or less, within 3 seconds or less, within 2 seconds or less, within 1 second or less, within 0.5 seconds or less, within 0.25 seconds or less, and within 0.1 seconds or less.

2.0 Introduction

FIGS. 1A and 1B are anterior and posterior views, respectively, of a human heart H. As shown in FIGS. 1A and 1B, the heart H comprises four chambers, the right atrium RA, the left atrium LA, the right ventricle RV, and the left ventricle LV. The right and left atria RA, LA are separated from the right and left ventricles RV, LV by a groove known as the coronary or atrioventricular sulcus AVS. The anterior interventricular sulcus AIS and posterior interventricular sulcus PIS are grooves that separate the right and left ventricles RV, LV. Each of the atrioventricular sulcus AVS, the anterior interventricular sulcus AIS, and posterior interventricular sulcus PIS are surrounded by epicardial fat pads FP. The great cardiac vein GCV begins near the apex A of the heart and extends in a superior direction within the anterior interventricular sulcus AIS until eventually curving around the left side of the heart H within the atrioventricular sulcus AVS. A posterior portion of the great cardiac vein GCV empties into the coronary sinus CS, which is also positioned within the atrioventricular sulcus AVS.

3.0 Overview

FIG. 2A schematically illustrates a representative treatment system 100 for improving contractility of a patient's heart H, arranged relative to the general anatomy of a patient's heart H and chest region. As shown in FIG. 2A, parasympathetic innervation of the heart muscle is partially controlled by the vagus nerve V, which has branches that feed into one or more plexuses N located on, in and/or adjacent the epicardial fat pads FP. The treatment system 100 includes a signal delivery system 101 having a signal generator 102 (e.g., a pulse generator) and a signal delivery device or element 104. The signal generator 102 can be connected directly to the signal delivery element 104, or it can be coupled to the signal delivery element 104 via a signal link 108 (e.g., an extension). In one embodiment, signal generator 102 can be connected to signal delivery element 104 via wireless signal communication or wireless signal transmission. In some embodiments, the signal generator 102 may be implanted subcutaneously within a patient P, while in other embodiments signal generator 102 can be external to the patient. As shown in FIG. 2A, the signal delivery element 104 is configured to be positioned at or proximate to an epicardial fat pad FP, and to apply an electrical signal to the adjacent vagal plexus N. It is believed that high frequency modulation at or proximate the epicardial fat pads FP can modulate the parasympathetic nerve plexus(es) N located on or within the epicardial fat pads FP, thereby improving parasympathetic tone (e.g., the electrical activity of the parasympathetic nerve fibers) and ventricular contraction strength. As such, in one embodiment, the electrical signal applied to the vagal plexus N is a high frequency electrical signal (or high frequency therapy signal).

The signal generator 102 can transmit signals (e.g., electrical signals or therapy signals) to the signal delivery element 104 that up-regulate (e.g., stimulate or excite) and/or down-regulate (e.g., block or suppress) target nerves (e.g., local vagal nerves). As used herein, and unless otherwise noted, to “modulate,” “stimulate,” or provide “modulation” or “stimulation” to the target nerves refers generally to having either type of the foregoing effects on the target nerves. The signal generator 102 can include a machine-readable (e.g., computer-readable) medium containing instructions for generating and transmitting suitable therapy signals. The signal generator 102 and/or other elements of the treatment system 100 can include one or more processors 110, memories 112 and/or input/output devices. Accordingly, the process of providing electrical signals, detecting physiological parameters of the patient, determining ejection fraction, adjusting the modulation signal, and/or executing other associated functions can be performed by computer-executable instructions contained by computer-readable media located at the signal generator 102 and/or other system components. The signal generator 102 can include multiple portions, elements, and/or subsystems (e.g., for directing signals in accordance with multiple signal delivery parameters) housed in a single housing, as shown in FIG. 2A, or in multiple housings.

The signal delivery system 101 can include one or more sensing elements 140 for detecting one or more physiological parameters of the patient before, during, and/or after the application of electrical therapy signals. In some embodiments, one or more of the sensing elements 140 can be carried by the signal generator 102, the signal delivery element 104, and/or other implanted components of the system 101. In other embodiments, the sensing element(s) 140 can be an extracorporeal or implantable device separate from the signal generator 102 and/or signal delivery element 104. Representative sensing elements 140 include one or more of: an electrocardiogram (“ECG”) unit, an impedance cardiography unit, a subcutaneous sensor, a ventricular sensor, an activity sensor (e.g., an accelerometer), a ventricular intracardiac sensor, an atrial intracardiac sensor, a temperature sensor, a flow rate sensor, a chemical sensor, a biosensor, an electrochemical sensor, a hemodynamic sensor, an optical sensor and/or other suitable sensing devices. Physiological parameters detected by the sensing element(s) 140 include heart rate, blood pressure, blood flow rate, activity level, ECG readings, impedance cardiography readings, ventricular and/or atrial pressure, and/or any correlates and/or derivatives of the foregoing parameters (e.g., raw data values, including voltages and/or other directly measured values).

In a representative embodiment, the signal delivery system 101 is configured to operate in either a “calibration mode” or an “active mode.” In the calibration mode, the signal delivery system 101 is configured to apply a low frequency electrical signal (also referred to herein as the “LF calibration signal”) via the signal delivery element 104 at the treatment site to determine a representative (e.g., maximum) signal amplitude that can be applied during subsequent treatment. In one embodiment, for example, the maximum signal amplitude is determined during the calibration mode to be the lower of: (1) the amplitude at which direct, immediate changes are observed to the heart rate, myocardial activation, or chamber sequencing, and (2) the amplitude which creates sensations which are perceived by the patient. In a particular embodiment, the signal delivery system 101 is also configured to apply a high frequency electrical signal (referred to herein as the “HF calibration signal”) when in the calibration mode to validate the maximum signal amplitude identified by the LF calibration signal. In the active mode, the signal delivery system 101 is configured to apply a high frequency electrical signal (also referred to herein as the “HF treatment signal” or “HF therapy signal”) at the treatment site to modulate the parasympathetic nerves proximate the treatment site. Parameters of the electrical signals applied by the signal delivery system 101 during calibration mode and/or active mode can be (1) automatically adjusted in response to a feedback mechanism and/or in accordance with a preset program (described in greater detail with reference to FIGS. 3-5), (2) manually adjusted in accordance with patient and/or practitioner inputs, and/or (3) automatically adjusted in a random or pseudorandom manner. “For example, a physician may find it beneficial to reduce the likelihood of the targeted nerves developing an adaptive, neuroplastic response that could diminish the efficacious effects of the applied signal over time. In such cases, an algorithm may be used to alter the applied amplitude of energy delivery in a pseudorandom manner. For example, the physician may set boundaries for the signal amplitude, such as a lower boundary of 0 mA and an upper boundary determined during calibration. Additionally, the physician may specify a schedule for varying the amplitude within the preset bounds, such as one amplitude change every N beats during the ventricular refractory period, M changes every beat during the ventricular refractory period, etc. Signal parameters include, for example, frequency, amplitude, pulse width, and duty cycle. It will be appreciated that in other embodiments, the signal delivery system 101 can be configured to operate in more than two modes.

In some embodiments, the signal generator 102 can obtain power to generate the therapy signals from an external power source 114. The external power source 114 can transmit power to the implanted signal generator 102 using electromagnetic induction (e.g., RF signals). For example, the external power source 114 can include an external coil 116 that communicates with a corresponding internal coil (not shown) within the implantable signal generator 102. The external power source 114 can be portable for ease of use.

In another embodiment, the signal generator 102 can obtain the power to generate therapy signals from an internal power source, in addition to or in lieu of the external power source 114. For example, the implanted signal generator 102 can include a non-rechargeable battery or a rechargeable battery to provide such power. When the internal power source includes a rechargeable battery, the external power source 114 can be used to recharge the battery. The external power source 114 can in turn be recharged from a suitable power source (e.g., conventional wall power).

During at least some procedures, an external programmer 120 (e.g., a trial modulator) can be coupled to the signal delivery element 104 during an initial procedure, prior to implanting the signal generator 102. For example, a practitioner (e.g., a physician and/or a company representative) can use the external programmer 120 in calibration mode to vary the signal parameters provided to the signal delivery element 104 in real-time, and select optimal or particularly efficacious signal parameters and/or signal delivery element 104 placement, as discussed in greater detail below with reference to FIG. 4. In a typical process, the practitioner uses a cable assembly 128 to temporarily connect the external programmer 120 to the signal delivery element 104. Whether calibrating the signal delivery system 101 or applying the HF treatment signal, the practitioner can test the efficacy of the signal delivery element 104 in an initial position and/or with initial signal parameters. The practitioner can then disconnect the cable assembly 128 (e.g., at a connector 130), reposition the signal delivery element 104, and reapply the electrical signal. This process can be performed iteratively until the practitioner confirms the desired therapy signal parameters and/or position for the signal delivery element 104 are clinically effective. Optionally, the practitioner can move the partially implanted signal delivery element 104 without disconnecting the cable assembly 128.

After a trial period with the external programmer 120, the practitioner can implant the implantable signal generator 102 within the patient P for longer term treatment. The signal delivery parameters provided by the signal generator 102 can still be updated after the signal generator 102 is implanted, via a wireless physician's programmer 124 (e.g., a physician's remote).

FIG. 2B is a partially schematic illustration of the heart H along with a signal delivery element 104 implanted within the great cardiac vein GCV. The parasympathetic nerve fibers N depicted in FIG. 2A are not shown in FIG. 2B for purposes of clarity. In the representative embodiment, the signal delivery element 104 comprises a flexible, isodiametric lead or lead body that carries features or elements for delivering an electrical signal to the treatment site after implantation. As used herein, the terms “lead” and “lead body” include any of a number of suitable substrates and/or support members that carry devices for providing therapy signals to the patient. For example, the lead body can include one or more electrodes or electrical contacts 105 that direct electrical signals into the patient's tissue, such as to improve parasympathetic tone (e.g., parasympathetic electrical activity). In other embodiments, the signal delivery element 104 can include devices other than a lead body (e.g., a paddle) and/or other lead configurations (e.g., cardiac pacing leads, implantable cardioverter defibrillator (ICD) leads, cardiac resynchronization therapy (CRT) leads, left heart leads, epicardial leads, etc.) that also direct electrical signals and/or other types of signals to the patient. In a particular embodiment, the signal delivery system 101 (FIG. 2A) includes more than one signal delivery element 104 (e.g., two signal delivery elements 104, three signal delivery elements 104, four signal delivery elements 104, etc.), each configured to apply electrical signals at different locations and/or coordinate signal delivery to deliver a combined signal to the same (or generally the same) anatomical location.

As shown in FIG. 2B, the signal delivery element 104 can be positioned along at least a portion of the great cardiac vein GCV at or proximate the anterior interventricular sulcus AIS. In other embodiments, the signal delivery element 104 can be positioned at other cardiac locations at or proximate the epicardial fat pads FP. As used herein, “at or proximate the epicardial fat pads” refers to a position of the signal delivery element 104 that is in, on or otherwise in direct contact with a coronary vessel that is in direct contact with the targeted epicardial fat pad FP, and/or in direct contact with the adipocyte tissue of the targeted fat pad FP. For example, the signal delivery element 104 can be directly coupled to the fat pad FP tissue, positioned within a coronary artery, positioned within a coronary vein not in direct contact with the targeted epicardial fat pad FP and/or in direct contact with the adipocyte tissue of the targeted fat pad FP (e.g., the middle cardiac vein, the small cardiac vein, one or more anterior cardiac veins, the coronary sinus, etc.), positioned at an exterior portion of a coronary artery and/or coronary vein, positioned along at least a portion of the great cardiac vein GCV apart from the anterior interventricular sulcus AIS (e.g., at or proximate the atrioventricular sulcus AVS, etc.), and/or other suitable locations. In some embodiments, the signal delivery element 104 can be positioned on or within a coronary blood vessel such that the signal delivery element 104 spans more than one portion of the host blood vessel. For example, the signal delivery element 104 can be positioned such that (a) a first portion of the signal delivery element 104 coincides with at least a portion of the great cardiac vein GCV at or proximate the anterior interventricular sulcus AIS, and (b) a second portion of the signal delivery element 104 coincides with at least a portion of the great cardiac vein GCV at or proximate the atrioventricular sulcus AVS. In particular embodiments, the signal delivery element 104 can be coupled to and/or apply an electrical signal to more than one type of tissue (e.g., the adipose tissue of the fat pads FP and the neural tissue of the parasympathetic plexus N (FIG. 2A), the connective tissue of the blood vessel(s) and the neural tissue of the parasympathetic plexus N, etc.).

4.0 Representative Embodiments

FIGS. 3-5 illustrate a representative method for treating CHF and/or improving cardiac contractility utilizing the treatment system 100 described above with reference to FIGS. 2A and 2B. FIG. 3 illustrates an overall process 300 in accordance with a particular embodiment of the disclosure. The overall process 300 includes determining a representative (e.g., maximum) treatment amplitude (process portion 310), applying an HF treatment signal to a patient via the signal delivery system 101 (FIG. 2A) (process portion 312), and automatically detecting one or more physiological parameters of the patient (process portion 314). The process 300 can further include automatically determining an ejection fraction of the patient's heart based on the detected physiological parameter (process portion 316) and, based on the determined ejection fraction, automatically adjusting one or more parameters of the HF treatment signal (process portion 318). FIGS. 4 and 5 describe further aspects of particular embodiments of the foregoing process.

FIG. 4 is a block diagram 400 illustrating a representative method for determining a representative (e.g., maximum) signal amplitude prior to modulating the nerves to prevent unwanted effects on the electrical conduction system of the heart (e.g., tachycardia, bradycardia, etc.) during treatment. In block 410, with the signal delivery system 101 (FIG. 2A) in calibration mode, the practitioner applies the calibration signal to the treatment site. In the embodiment shown, an LF calibration signal is applied. In an alternative embodiment, however, a HF calibration signal may be applied. In a particular embodiment, the LF calibration signal can have a frequency of from about 0.1 to about 2.5 Hz, and in some embodiments, less than 1 Hz. In some embodiments the LF calibration signal can have a pulse width greater than 600 microseconds, and in certain embodiments, of from about 100 microseconds to about 2.5 milliseconds. During application of the LF calibration signal, the practitioner and/or system processor 110 can monitor an ECG of the patient for any changes (e.g., timing changes in the PQRST wave) while increasing the amplitude of the applied signal from a starting amplitude value (e.g., starting at an amplitude of 0.1 mA and increasing the amplitude in increments; for example of 0.1 mA, 0.2 mA, 0.5 mA, or 1.0 mA). As indicated by blocks 412 and 414, as long as no cardiac effect is detected on the ECG, the practitioner and/or processor 110 (FIG. 2A) can continue to increase the amplitude of the LF calibration signal. As indicated by blocks 412 and 416, if at any point the practitioner and/or system processor 110 detects a change in the ECG, the amplitude of applied signal can cease to increase and the amplitude at which the change in the ECG was detected is automatically stored in system memory 112 (FIG. 2A) (e.g., within the signal generator 102 (FIG. 2A) and/or the external programmer 120 (FIG. 2A)) and/or manually entered by the practitioner.

In a particular embodiment, the signal delivery system 101 (FIG. 2A) is optionally configured to determine a representative (e.g., maximum) HF signal amplitude by applying an HF calibration signal to the treatment site and monitoring the patient's ECG while increasing the HF calibration signal's amplitude from a starting amplitude value. In some embodiments, the HF calibration signal has a pulse width less than or equal to 1/(2*(the frequency of the HF calibration signal), and in a particular embodiment, of from about 100 nanoseconds to less than or equal to 1/(2*(the frequency of the HF calibration signal). In other embodiments, the signal can have other suitable pulse widths. Similar to the LF calibration process 400, as long as no cardiac effect is detected on the ECG, the practitioner and/or processor 110 (FIG. 2A) continues to increase the amplitude of the HF calibration signal. If at any point the practitioner and/or system processor 110 detects a change in the ECG, the amplitude of applied HF calibration signal can cease to increase and the amplitude at which the change in the ECG was detected is automatically stored in system memory 112 (FIG. 2A) (e.g., within the signal generator 102 (FIG. 2A) and/or the external programmer 120 (FIG. 2A)) and/or manually input by the practitioner. Although it is expected that the electrical energy required to trigger cardiac activity at the LF calibration signal will be much lower than the electrical energy required at the HF calibration signal, it can be advantageous in some procedures to determine the maximum treatment amplitude with the HF calibration signal to validate the maximum treatment signal amplitude determined using the LF calibration signal. Moreover, in some instances the physician may use the HF calibration signal to set the upper and lower bounds of the HF treatment signal amplitude. For example, in some embodiments the upper bound of the HF treatment signal amplitude can be set to the representative LF calibration signal amplitude plus 0.5*(the representative HF calibration signal amplitude minus the representative LF calibration signal amplitude). In yet other embodiments, the physician may set the HF treatment signal amplitude upper bound to 0.9*(the LF calibration signal amplitude).

Once the maximum treatment signal amplitude has been determined, the system 101 (FIG. 2A) can be put in active mode (as indicated in FIG. 3). In active mode, the signal delivery system 101 is configured to apply a therapy signal to the treatment site. Without being bound by theory, HF signals are believed to have significantly improved therapeutic effects when compared to LF signals in modulating the vagal nerve at the heart because it is believed that the LF signal parameters required for an LF signal to therapeutically modulate the vagal nerve would also necessarily activate the myocardium and induce unwanted cardiac effects (e.g., tachycardia, bradycardia, etc.). In some embodiments, an HF treatment signal is applied and can have a starting amplitude of about 90% of the maximum signal amplitude (determined during calibration mode). In a representative embodiment, the HF treatment signal is a pulse train with a duty-cycle from about 1% on to about 90% on (e.g., 10% or about 10% on, 25% or about 25% on, 50% or about 50% on, 70% or about 70% on, etc.). The HF treatment signal can have a pulse width of from about 1 μs to about 80 μs, and in some embodiments, of from about 20 μs to about 60 μs (e.g., 30 μs, 37 μs, 42 μs, etc.). The HF treatment signal can also have an interpulse width of from about 0 μs to about 50 μs, or of from about 10 μs to about 40 μs. In other embodiments, the HF treatment signal can be any charge-balanced, alternating-current waveform, such as a bi-phasic waveform, a sine waveform, a square waveform, a triangular waveform, a rectangular waveform, etc. In yet other embodiments, the treatment signal is not pulsed and instead is delivered continuously. In such embodiments, charge balancing can be achieved via active recharge on a pulse-by-pulse basis. As discussed in greater detail below with reference to FIG. 5, the signal delivery system 101 can control the timing of the application of the HF treatment signal based on one or more feedback mechanisms and/or preset programs (e.g., based on time of day). For example, the system 101 can be programmed to deliver the HF treatment signal for seconds, minutes, hours, days, weeks, and/or months at a time. In these and other embodiments, the signal delivery system 101 can be configured to apply the HF treatment signal continuously while implanted.

Application of the HF treatment signal at the treatment site (e.g., at or proximate an epicardial fat pad) is expected to modulate one or more vagal nerves at or proximate to the treatment site, thereby improving parasympathetic tone and cardiac contractility. One way to assess contractility and/or the efficacy of the treatment is by measuring ejection fraction, or the percentage of blood pumped out of the heart during each beat. An increase in ejection fraction indicates improved contractility and, likewise, a decrease in ejection fraction indicates reduced contractility. Under resting conditions, healthy adults have an average ejection fraction between 50% and 75%. Below 50%, the patient may experience a variety of symptoms, including shortness of breath, inability to exercise, swelling of the feet and lower legs, fatigue, weakness, and rapid or irregular heartbeat. Below 30%, the patient's quality of life is minimal and death may be imminent.

When the signal delivery system 101 (FIG. 2A) is in active mode—whether applying the treatment signal or not—the treatment system 100 and/or signal delivery system 101 can be configured to continuously or intermittently monitor one or more physiological parameters of the patient via the one or more sensing elements 140 (FIG. 2A). In a representative embodiment, the sensing element(s) 140 are positioned and/or otherwise configured to sense one or more physiological parameters that, when analyzed together by the processor 110, provide a reliable, real-time estimate of ejection fraction that can be used to adjust the treatment signal. Such physiological parameters include systolic pressure, diastolic pressure, interatrial pressure, flow rate, arterial pressure, heart rate, ventricular volume, ventricular impedance, blood oxygen saturation, and/or any derivative of the foregoing. In a particular embodiment, for example, the system 101 includes an algorithm that continuously and/or iteratively monitors ventricular impedance and heart rate and, based on those parameters, determines a change in ventricular volume over time (dVV/dt). In another embodiment, the system 101 includes one or more transducers configured for echocardiographic signaling. For example, in some embodiments the signal delivery element 104 (FIG. 2A) includes an array of piezoelectric transducers configured to emit sound waves towards one or more chambers of the heart, detect the reflected sound waves, and convert the reflected sound waves into a signal for storage and/or processing by the processor 110 (FIG. 2A). In these and other embodiments, the system 101 can include one or more transducers separate from the signal delivery element 104 and configured to be positioned at or near the heart and/or other internal and/or external anatomical locations. It will be appreciated that the system 101 can include multiple algorithms for determining and/or estimating ejection fraction. For example, in a particular embodiment, the system 101 can include an algorithm that estimates ejection fraction by monitoring changes in contraction velocity (e.g., via an accelerometer at the lead).

FIG. 5 is a block diagram 500 illustrating a method for adjusting the timing and/or one or more other parameters of the treatment signal in response to real-time ejection fraction feedback. As indicated at blocks 510 and 512, when the signal delivery system 101 is in active mode, the sensing element(s) 140 (FIG. 2A) continuously or intermittently communicate the sensed parameter values to the system processor 110 (FIG. 2A) and/or memory 112 (FIG. 2A). The processor 110 can determine an ejection fraction measurement (also referred to herein as the “EF measurement”) based on the sensed parameters (block 512). The EF measurement can be an instantaneous ejection fraction value or set of values, an average ejection fraction value over a period of time, and/or any derivative or correlate of either of the foregoing, such as a change in ejection fraction over time (dEF/dt) (or lack thereof) and a rate of change of ejection fraction EF over time (d²EF/dt²) (or lack thereof).

In block 514, the processor 110 (FIG. 2A) compares the EF measurement with a target ejection fraction threshold (also referred to herein as “target EF threshold”). The target EF threshold is a standardized or patient-specific ejection fraction metric that represents an improvement in ejection fraction relative to the patient's ejection fraction prior to treatment. The target EF threshold can be a single value or range of values, and can be determined prior to treatment and/or adjusted during treatment. Similar to the EF measurement, the target EF threshold can be an instantaneous ejection fraction value or set of values, an average ejection fraction value over a period of time, and/or any derivative of either of the foregoing, such as a change in ejection fraction over time (dEF/dt) (or lack thereof) and a rate of change of ejection fraction over time (d²EF/dt²) (or lack thereof). Moreover, on some embodiments the system 101 (FIG. 2A) may take into account multiple different EF measurements and/or multiple different target EF thresholds at decision block 514, and/or require more than one comparison before choosing a course of action.

As indicated by block 530, if the EF measurement is less than the target EF threshold, the processor 110 (FIG. 2A) will take one of two actions based on whether the signal delivery system 101 (FIG. 2A) is currently applying a treatment signal. If the EF measurement is less than the target EF threshold and the signal delivery system 101 is presently applying the treatment signal, one or more parameters of the treatment signal may not be sufficient to modulate the parasympathetic nerves. In such a scenario (indicated by block 544), the processor 110 can adjust one or more signal parameters (e.g., increase the treatment signal amplitude and/or the pulse width of the treatment signal) to increase the intensity of the treatment signal. As indicated by blocks 540 and 542, the processor 110 will not increase the treatment signal magnitude if the maximum treatment signal amplitude has already been reached. Alternatively, if the EF measurement is less than the target EF threshold and the signal delivery system 101 is not presently applying the treatment signal, then the processor 110 can initiate application of the treatment signal.

As indicated by block 520, if the EF measurement is greater than or equal to the target EF threshold, the processor 110 (FIG. 2A) will take one of two actions based on whether the signal delivery system 101 (FIG. 2A) is currently applying a treatment signal. If the EF measurement is greater than the target EF threshold and the signal delivery system 101 is presently applying the treatment signal, it may be beneficial to cease applying the treatment signal (indicated by block 526) but continue monitoring ejection fraction should the EF measurement fall below the target EF threshold. Alternatively, if the EF measurement is greater than the target EF threshold and the signal delivery system 101 is not presently applying the treatment signal, then the processor 110 can continue to not apply the treatment signal (indicated by block 524) but monitor ejection fraction should the EF measurement fall below the target EF threshold.

It will be appreciated that in any of the above embodiments, the signal delivery system 101 (FIG. 2A) can measure other parameters (in addition to ejection fraction) and can additionally or alternatively adjust the timing and/or signal parameters of the treatment signal in response to such other measurements and/or any parameter sensed by the sensing elements 140. For example, the signal delivery system 101 can be configured to detect an average heart rate outside of a target heart rate threshold, and, for example, if the detected heart rate is greater than the target heart rate threshold while the treatment signal is being applied, the processor 110 can decrease the pulse width and/or increase the amplitude of the treatment signal in order to increase the parasympathetic tone.

5.0 Additional Embodiments

Embodiments of the presently disclosed technology are described in the following examples. A method for treating congestive heart failure in a patient in accordance with one example includes applying an electrical signal to the patient via a treatment system that includes a signal delivery element in electrical communication with the patient's vagus nerve at a portion of the vagus nerve located at or proximate to the anterior interventricular junction of the patient's heart, with the electrical signal having a frequency of from about 1 kHz to about 100 kHz. The method further includes automatically detecting at least one physiological parameter of the patient, automatically determining at least one of an ejection fraction of the patient's heart and a correlate of the ejection fraction based on the detected parameter, and automatically adjusting the applied signal based on the determined ejection fraction. In some embodiments of the method, automatically adjusting the applied signal includes stopping the application of the applied signal in response to detecting an ejection fraction greater than or equal to a target ejection fraction threshold. In these and other embodiments, automatically adjusting the applied signal includes increasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction less than a target ejection fraction threshold and/or automatically adjusting the applied signal includes decreasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction greater than or equal to a target ejection fraction threshold. In some embodiments, automatically detecting a physiological parameter includes automatically detecting the patient's heart rate, and automatically adjusting the applied signal includes increasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to the increase in the patient's heart rate. Further, in at least some embodiments of the method, applying the electrical signal occurs at a first time and automatically adjusting the applied signal includes applying the electrical signal at a second time in response to detecting an ejection fraction less than the target ejection fraction threshold. In a particular embodiment, applying the electrical signal includes applying the signal to the patient via a lead positioned at or proximate to the atrial-ventricular fat pads of the patient's heart. In certain embodiments of the method, applying the electrical signal includes applying the signal with a pulse width less than or equal to 1/(2×the frequency of the signal). In further embodiments, the treatment system includes an implantable treatment system. In yet further embodiments, the at least one detected physiological parameter includes at least one of the patient's heart rate, the patient's blood pressure, and the patient's blood flow rate.

A method for treating congestive heart failure in a patient in accordance with another representative example includes applying an electrical signal having a frequency of from about 1 kHz to about 100 kHz to an epicardial fat pad of the patient's heart, automatically monitoring an ejection fraction of the patient, automatically comparing the monitored ejection fraction value to a predetermined threshold, and based on the comparison, automatically adjusting the applied signal. In some embodiments of the method, automatically adjusting the applied signal includes stopping the application of the applied signal in response to detecting an ejection fraction greater than or equal to a target ejection fraction threshold. In these and other embodiments, automatically adjusting the applied signal includes increasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction less than a target ejection fraction threshold and/or automatically adjusting the applied signal includes decreasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction greater than or equal to a target ejection fraction threshold. In a particular embodiment of the method, applying the electrical signal occurs at a first time, and wherein automatically adjusting the applied signal includes applying the electrical signal at a second time in response to detecting an ejection fraction less than the target ejection fraction threshold.

Still a further representative example of a system for treating congestive heart failure in a patient in accordance with the present technology includes an electrical signal generator having a computer readable storage medium, and an implantable signal delivery element coupled to the signal generator. The signal generator can be configured to be positioned proximate an epicardial fat pad of the patient and apply an electrical signal having a frequency of from about 1 kHz to about 100 kHz to neural tissue proximate and/or within the epicardial fat pad. In some embodiments of the system, the computer-readable storage medium has instructions that, when executed, determine an ejection fraction of the patient's heart in real-time and adjust the signal applied by the signal delivery element in response to the determined ejection fraction. In a particular embodiment, the system further comprises a sensor in communication with the computer-readable storage medium. In at least some of such embodiments, the sensor is configured to detect a physiological parameter of the patient, and the instructions, when executed, calculate the ejection fraction based on the physiological parameter. In a certain embodiment of the system, the signal generator is an implantable signal generator. In further embodiments of the system, the instructions, when executed, and in response to a determined ejection fraction greater than or equal to a predetermined target threshold, cease to apply the electrical signal. In these and other embodiments, the instructions, when executed, and in response to a determined ejection fraction less than or equal to a predetermined target threshold, start application of the electrical signal and/or in response to a determined ejection fraction less than or equal to a predetermined target threshold, increase at least one of an amplitude or a pulse width of the electrical signal. In a representative embodiment of the system, the signal delivery element is configured to be positioned within a coronary blood vessel of the patient.

From the foregoing, it will be appreciated that specific embodiments of the disclosed technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the technology. For example, in some embodiments the system 101 (FIG. 2A) can be configured to deliver pacing signals to the heart. In such embodiments, for example, the system 101 can include a single signal generator configured to transmit pacing signals and modulating signals, or the system 101 can include a modulating signal generator (e.g., signal generator 102 (FIG. 2A) and a separate pacing signal generator (e.g., external or implantable). In those embodiments having a single signal generator configured to transmit pacing and modulating signals, the system 101 can include one or more signal delivery element(s) configured to deliver pacing signals, modulating signals, or both.

Certain aspects of the technology described in the context of particular embodiments may be combined or eliminated in other embodiments. For example, in some embodiments the signal generator 102 (FIG. 2A) is configured to only transmit LF or HF signals in calibration mode, and in other embodiments the signal generator 102 may not include a calibration mode. Further, while advantages associated with certain embodiments of the disclosed technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein.

To the extent any materials incorporated herein by reference conflict with the present disclosure, the present disclosure controls. 

I/we claim:
 1. A method for treating congestive heart failure in a patient, comprising: applying an electrical signal to the patient via a treatment system that includes a signal delivery element in electrical communication with the patient's vagus nerve at a portion of the vagus nerve located at or proximate to the anterior interventricular junction of the patient's heart, the electrical signal having a frequency in a range of from about 1 kHz to about 100 kHz; automatically detecting at least one physiological parameter of the patient; based on the detected parameter, automatically determining an ejection fraction indicator that is at least one of an ejection fraction of the patient's heart and a correlate of the ejection fraction; and automatically adjusting the applied signal based on the determined ejection fraction indicator.
 2. The method of claim 1 wherein automatically adjusting the applied signal includes stopping the application of the applied signal in response to detecting an ejection fraction indicator greater than or equal to a target ejection fraction threshold.
 3. The method of claim 2 wherein applying the electrical signal occurs at a first time, and wherein automatically adjusting the applied signal includes applying the electrical signal at a second time in response to detecting an ejection fraction indicator less than the target ejection fraction threshold.
 4. The method of claim 1 wherein automatically adjusting the applied signal includes increasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction indicator less than a target ejection fraction threshold.
 5. The method of claim 1 wherein automatically adjusting the applied signal includes decreasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction indicator greater than or equal to a target ejection fraction threshold.
 6. The method of claim 1 wherein: automatically detecting a physiological parameter includes automatically detecting the patient's heart rate; and automatically adjusting the applied signal includes increasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to the increase in the patient's heart rate.
 7. The method of claim 1 wherein applying the electrical signal includes applying the signal to the patient via a lead positioned at or proximate to the atrial-ventricular fat pads of the patient's heart.
 8. The method of claim 1 wherein applying the electrical signal includes applying the signal with a pulse width less than or equal to 1/(2×the frequency of the signal).
 9. The method of claim 1 wherein the treatment system includes an implantable treatment system.
 10. The method of claim 1 wherein the at least one detected physiological parameter includes at least one of the patient's heart rate, the patient's blood pressure, and the patient's blood flow rate.
 11. A method for treating congestive heart failure in a patient, comprising: applying an electrical signal to an epicardial fat pad of the patient's heart, the applied signal having a frequency of from about 1 kHz to about 100 kHz; automatically monitoring an ejection fraction of the patient; automatically comparing the monitored ejection fraction value to a predetermined threshold; and based on the comparison, automatically adjusting the applied signal.
 12. The method of claim 11 wherein automatically adjusting the applied signal includes stopping the application of the applied signal in response to detecting an ejection fraction greater than or equal to a target ejection fraction threshold.
 13. The method of claim 12 wherein applying the electrical signal occurs at a first time, and wherein automatically adjusting the applied signal includes applying the electrical signal at a second time in response to detecting an ejection fraction less than the target ejection fraction threshold.
 14. The method of claim 11 wherein automatically adjusting the applied signal includes increasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction less than a target ejection fraction threshold.
 15. The method of claim 11 wherein automatically adjusting the applied signal includes decreasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction greater than or equal to a target ejection fraction threshold.
 16. A system for treating congestive heart failure in a patient, comprising: an electrical signal generator having a computer readable storage medium; an implantable signal delivery element coupled to the signal generator, wherein the signal delivery element is configured to be positioned proximate an epicardial fat pad of the patient and apply an electrical signal having a frequency in a range of from about 1 kHz to about 100 kHz to neural tissue proximate and/or within the epicardial fat pad; and wherein the computer-readable storage medium has instructions that when executed: determine in real-time at least one of an ejection fraction of the patient's heart and a correlate of the ejection fraction; and adjust the signal applied by the signal delivery element in response to the determined ejection fraction.
 17. The system of claim 16, further comprising a sensor in communication with the computer-readable storage medium, wherein the sensor is configured to detect a physiological parameter of the patient, and wherein the instructions, when executed, calculate the ejection fraction based on the physiological parameter.
 18. The system of claim 16 wherein the signal generator is an implantable signal generator.
 19. The system of claim 16 wherein the instructions, when executed, and in response to a determined ejection fraction greater than or equal to a predetermined target threshold, cease to apply the electrical signal.
 20. The system of claim 16 wherein the instructions, when executed, and in response to a determined ejection fraction less than or equal to a predetermined target threshold, start application of the electrical signal.
 21. The system of claim 16 wherein the instructions, when executed, and in response to a determined ejection fraction less than or equal to a predetermined target threshold, increase at least one of an amplitude or a pulse width of the electrical signal.
 22. The system of claim 16 wherein the signal delivery element is configured to be positioned within a coronary blood vessel of the patient.
 23. A method for treating congestive heart failure in a patient, comprising: applying an electrical signal to the patient via a treatment system that includes a signal delivery element positioned at an epicardial fat pad of the patient's heart, the electrical signal having a frequency in a range of from about 1 kHz to about 100 kHz; automatically detecting at least one physiological parameter of the patient via one or more sensing elements; based on the detected parameter, automatically determining an ejection fraction indicator that is at least one of an ejection fraction of the patient's heart and a correlate of the ejection fraction; and automatically adjusting the applied signal based on the determined ejection fraction indicator.
 24. The method of claim 23 wherein automatically adjusting the applied signal includes stopping the application of the applied signal in response to detecting an ejection fraction indicator greater than or equal to a target ejection fraction threshold.
 25. The method of claim 23 wherein applying the electrical signal occurs at a first time, and wherein automatically adjusting the applied signal includes applying the electrical signal at a second time in response to detecting an ejection fraction indicator less than the target ejection fraction threshold.
 26. The method of claim 23 wherein automatically adjusting the applied signal includes increasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction indicator less than a target ejection fraction threshold.
 27. The method of claim 23 wherein automatically adjusting the applied signal includes decreasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction indicator greater than or equal to a target ejection fraction threshold.
 28. The method of claim 23 wherein: automatically detecting a physiological parameter includes automatically detecting the patient's heart rate; and automatically adjusting the applied signal includes increasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to the increase in the patient's heart rate.
 29. The method of claim 23 wherein applying the electrical signal includes applying the signal to the patient via a lead positioned at or proximate to the atrial-ventricular fat pads of the patient's heart.
 30. The method of claim 23 wherein applying the electrical signal includes applying the signal with a pulse width less than or equal to 1/(2×the frequency of the signal).
 31. The method of claim 23 wherein the treatment system includes an implantable treatment system.
 32. The method of claim 23 wherein the at least one detected physiological parameter includes at least one of the patient's heart rate, the patient's blood pressure, and the patient's blood flow rate.
 33. A system for treating congestive heart failure in a patient, comprising: an implantable electrical signal generator having a computer readable storage medium; an implantable signal delivery element coupled to the signal generator, wherein the signal delivery element is configured to be positioned at or proximate the patient's vagus nerve at a portion of the vagus nerve located at or proximate to the interventricular junction of the patient's heart, and wherein the signal delivery element is configured to apply an electrical signal having a frequency in a range of from about 1 kHz to about 100 kHz to neural tissue proximate the portion of the vagus nerve; and wherein the computer-readable storage medium has instructions that when executed: determine an ejection fraction indicator that is at least one of an ejection fraction of the patient's heart and a correlate of the ejection fraction; and adjust the signal applied by the signal delivery element in response to the determined ejection fraction indicator.
 34. The system of claim 33, further comprising a sensor in communication with the computer-readable storage medium, wherein the sensor is configured to detect a physiological parameter of the patient, and wherein the instructions, when executed, calculate the ejection fraction indicator based on the physiological parameter.
 35. The system of claim 33 wherein the instructions, when executed, and in response to a determined ejection fraction indicator greater than or equal to a predetermined target threshold, cease to apply the electrical signal.
 36. The system of claim 33 wherein the instructions, when executed, and in response to a determined ejection fraction indicator less than or equal to a predetermined target threshold, start application of the electrical signal.
 37. The system of claim 33 wherein the instructions, when executed, and in response to a determined ejection fraction indicator less than or equal to a predetermined target threshold, increase at least one of an amplitude or a pulse width of the electrical signal.
 38. The system of claim 33 wherein the signal delivery element is configured to be positioned within a coronary blood vessel of the patient.
 39. A system for treating congestive heart failure in a patient, comprising: an implantable electrical signal generator having a computer readable storage medium; an implantable signal delivery element coupled to the signal generator, wherein the signal delivery element is configured to be positioned at least partially within the coronary sinus of the patient's heart, and wherein the signal delivery element is configured to apply an electrical signal having a frequency in a range of from about 1 kHz to about 100 kHz to neural tissue proximate the coronary sinus; and wherein the computer-readable storage medium has instructions that when executed: determine an ejection fraction indicator that is at least one of an ejection fraction of the patient's heart and a correlate of the ejection fraction; and adjust the signal applied by the signal delivery element in response to the determined ejection fraction indicator.
 40. The system of claim 39, further comprising a sensor in communication with the computer-readable storage medium, wherein the sensor is configured to detect a physiological parameter of the patient, and wherein the instructions, when executed, calculate the ejection fraction indicator based on the physiological parameter.
 41. The system of claim 39 wherein the instructions, when executed, and in response to a determined ejection fraction indicator greater than or equal to a predetermined target threshold, cease to apply the electrical signal.
 42. The system of claim 39 wherein the instructions, when executed, and in response to a determined ejection fraction indicator less than or equal to a predetermined target threshold, start application of the electrical signal.
 43. The system of claim 39 wherein the instructions, when executed, and in response to a determined ejection fraction indicator less than or equal to a predetermined target threshold, increase at least one of an amplitude or a pulse width of the electrical signal.
 44. A method for treating congestive heart failure in a patient, comprising: applying an electrical signal to the patient via a treatment system that includes a signal delivery element positioned at least partially within the coronary sinus of the patient's heart, the electrical signal having a frequency in a range of from about 1 kHz to about 100 kHz; automatically detecting at least one physiological parameter of the patient via one or more sensing elements; based on the detected parameter, automatically determining an ejection fraction indicator that is at least one of an ejection fraction of the patient's heart and a correlate of the ejection fraction; and automatically adjusting the applied signal based on the determined ejection fraction indicator.
 45. The method of claim 44 wherein automatically adjusting the applied signal includes stopping the application of the applied signal in response to detecting an ejection fraction indicator greater than or equal to a target ejection fraction threshold.
 46. The method of claim 45 wherein applying the electrical signal occurs at a first time, and wherein automatically adjusting the applied signal includes applying the electrical signal at a second time in response to detecting an ejection fraction indicator less than the target ejection fraction threshold.
 47. The method of claim 44 wherein automatically adjusting the applied signal includes increasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction indicator less than a target ejection fraction threshold.
 48. The method of claim 44 wherein automatically adjusting the applied signal includes decreasing at least one of an amplitude of the applied signal and a pulse width of the applied signal in response to detecting an ejection fraction indicator greater than or equal to a target ejection fraction threshold. 